/Engine/Source/Runtime/MeshConversion/Public/MeshDescriptionBuilder.h
Set the specified value for the named attribute / vertex index combination. If a vertex attribute with the given name doesn't exist, it is created.
template<typename T> void SetVertexAttributeValue ( [FName](API\Runtime\Core\UObject\FName) AttributeName, [FVertexID](API\Runtime\MeshDescription\FVertexID) VertexID, const T & Value )